TF2 Gray Tease?

A "letter" on the Team Fortress 2 Website references a third son of Zepheniah Mann named Gray who was "absconded by that Scourge of London, the EAGLE." The NeoGAF Forums hash through the possibilities that this might mean we can expect a third Gray faction to join the teamplay shooter, or perhaps the Grays will be a robot hoard to battle both red and Blu forces in a Mann versus Machine mode. The letter says Gray's birthday is September 2nd (the final day of PAX and The International tournament), so some are speculating that date may be when this all comes together. Thanks Kotaku.